Refrigerant compositions

ABSTRACT

Refrigerant compositions are disclosed which comprise: (a) pentafluoroethane, octafluoropropane, trifluoromethoxydifluoromethane or hexafluoro-cyclopropane, or a mixture of two or more thereof, in an amount of at least 35% based on the weight of the composition, (b) 1,1,1,2- or 1,1,2,2-tetrafluoroethane, trifluoromethoxypentafluoroethane, 1,1,2,3,3-heptafluoropropane or a mixture of two or more thereof, in an amount of at least 30% by weight based on the weight of the composition and (c) n-butane or isobutane, in an amount from 1% to less than 2.3% by weight based on the weight of the composition.

[0001] The present invention relates to refrigerant compositions,particularly for use as replacements in refrigeration equipmentcurrently employing, or designed to employ, the refrigerants R12 andR22.

[0002] Refrigerant R12 (CCl₂F₂) has been a commonly used refrigerantespecially in domestic refrigerators. However, R12 contains chlorineatoms and has been implicated in environmental damage to the ozonelayer. As a result efforts have been made to replace R12 with arefrigerant formulation which does not involve the use of refrigerantssuch as R12 which contain chlorine atoms. Similar comments apply to R22which is used principally for air conditioning systems.

[0003] Among alternatives, particular attention has been directed atR134a (C₂H₂F₄; 1,1,1,2-tetrafluoroethane) along with pentafluoroethane(R125) (b.pt. −48.6° C.). Commercial formulations of these tworefrigerants involve the use of a hydrocarbon, namely propane, propyleneor isobutane. While these refrigerant formulations are generallyeffective as replacements for R12 and R22, nevertheless it has beenfound that their use is not entirely satisfactory.

[0004] Difficulty has arisen with the flammability of the fractionatedcomposition, that is to say the vapour above the liquid compositionpossesses flammability problems. As a result these commercialformulations can produce flammable compositions under some leak scenarioconditions. The flammability of these refrigerant compositions residesin their hydrocarbon content. One of the purposes of incorporating thehydrocarbon is so that the formulation is compatible with the lubricantsordinarily used in R12 and R22 refrigeration equipment. The specifichydrocarbons have been selected because they possess the correct boilingpoint in relation to that of the fluorocarbon.

[0005] In our GB 2327427 we describe and claim a refrigerant compositionwhich comprises

[0006] (a) R125, R218 (octafluoropropane; b.pt. −36.7° C.),trifluoromethoxydifluoromethane (b.pt. −34.6° C.) orhexafluoro-cyclopropane (b.pt. −31.5 ° C.), or a mixture of two or morethereof, in an amount from 5 to 60% by weight based on the weight of thecomposition

[0007] (b) R125, R134a, R134 (1,1,2,2-tetrafluoroethane),1,1-difluoroethane (R152a; b.pt. −24.7° C.),trifluoromethoxypentafluoroethane (b.pt. −23.3° C.),1,1,1,2,3,3,3-heptafluoropropane (R227ea; b.pt. −18.3° C.) or1,1,1,2,2,3,3-heptafluoropropane (R227ca; b.pt. −16.3° C.), or a mixtureof two or more thereof, in an amount from 30 to 94% by weight based onthe weight of the composition and

[0008] (c) an unsubstituted hydrocarbon of the formula C_(n)H_(m) inwhich n is at least 4 and m is at least 2n−2, other than methyl propane,in an amount from 1 to 10% by weight based on the weight of thecomposition.

[0009] Surprisingly if a hydrocarbon with at least 4 carbon atoms otherthan methyl propane (isobutane) is used instead of those previouslyadvocated the flammability of the fractionated composition is greatlyreduced.

[0010] Two specific formulations are mentioned in this application. Boththese formulations have 50% by weight of R134a and either 46.5% byweight of R125 and 4% by weight of n-butane or 46% by weight of R125 and3.5% by weight of n-butane. Experiments have been conducted withvariations in this formulation in order to assess their performance bothas regards their cooling capacity and their coefficient of performance.As would be expected, as the concentration of n-butane is reduced thecooling capacity generally reduces. However, surprisingly, according tothe present invention it has been found that below a particular level,about 2.3% by weight of n-butane, the performance increases again suchthat the performance at a concentration of only 1.5% by weight iscomparable to that of the formulation containing 3.5% by weight. It hasalso surprisingly been found that similar quantities of isobutane(methyl propane) is also very effective. Amounts greater than about 2.3%isobutane tend to give rise to flammability problems which do not ariseat lower concentrations. Accordingly, the present invention provides aliquid refrigerant composition which comprises (generally in the liquidphase):

[0011] (a) pentafluoroethane, octafluoropropane,trifluoromethoxydifluoromethane or hexafluoro-cyclopropane, or a mixtureof two or more thereof, in an amount of at least 35% based on the weightof the composition,

[0012] (b) 1,1,1,2- or 1,1,2,2-tetrafluoroethane,trifluoromethoxypentafluoroethane, 1,1,1,2,3,3-heptafluoropropane or amixture of two or more thereof, in an amount of at least 30% by weightbased on the weight of the composition and

[0013] (c) n-butane or isobutane, in an amount from 1% to less than 2.3%by weight based on the weight of the composition.

[0014] The present invention also provides a process for producingrefrigeration which comprises condensing a composition of the presentinvention and thereafter evaporating the composition in the vicinity ofa body to be cooled. The invention also provides a refrigerationapparatus containing, as refrigerant, a composition of the presentinvention.

[0015] Component (a) is present in an amount of at least 35% by weightbased on the weight of the composition. In practice, the concentrationwill generally be at least 40% by weight although a general range is 35to 65% by weight. A preferred range is 40 to 55% by weight, especially45 to 52% by weight. Preferably, component (a) is R125 or a mixturecontaining at least an half (by mass) of R125. In the latter case it isadvisable that the content of R125 in the total composition is at least35%, preferably 40%, by weight. Most preferably component (a) is R125.

[0016] Component (b) is present in the composition in an amount of atleast 30% by weight based on the weight of the composition. Typically,the component is present in an amount from 35% to 60% by weight,preferably 45 to 60% and especially 47.5 to 55% by weight. Component (b)is preferably R134a.

[0017] When component (a) is R125 and component (b) is R134a, thecontent of each is desirably 35 to 60% by weight, generally 40 to 60% byweight when component (c) is n-butane. Preferably the concentration ofeach is above 45 to 55% by weight.

[0018] The presence of at least one further component in the compositionis not excluded. Thus although, typically, the composition will comprisethe three essential components, a fourth component, at least, can alsobe present. Typical further components include hydrocarbons such aspropane as well as other fluorocarbons and, in particular,hydrofluorocarbons, such as those having a boiling point at atmosphericpressure of at most −40° C., preferably at most −49° C., especiallythose where the F/H ratio in the molecule is at least 1, preferably R23,trifluoromethane and, most preferably, R32, difluoromethane. In general,the maximum concentration of these other ingredients does not exceed 30%by weight, typically not exceeding 20%, preferably not exceeding 10% andespecially not exceeding 5% and more especially not exceeding 2%, byweight, based on the sum of the weights of components (a), (b) and (c).The presence of hydrofluorocarbons generally has a neutral effect on thedesired properties of the formulation. Desirably the butane, especiallyn-butane, represents at least 70%, preferably at least 80% and morepreferably at 90%, by weight of the total weight of hydrocarbons in thecomposition. It will be appreciated that it is preferable to avoidperhalocarbons so as to minimise any greenhouse effect.

[0019] It has been found that the compositions of the present inventionare highly compatible with the mineral oil lubricants which have beenconventionally used with CFC refrigerants. Accordingly the compositionsof the present invention can be used with mineral oil and alkyl benzenelubricants including naphthenic oils, paraffin oils and silicone oils,and there is no need to employ fully synthetic lubricants such as polyolesters (POE), polyalkyleneglycols (PAG) and polyoxypropylene glycolswhich are needed for many of the newer refrigerant compositions. Furtherdetails of suitable lubricants which can be employed are disclosed inEP-A-399817.

[0020] The usual additives can be used including “extreme pressure” andantiwear additives, oxidation and thermal stability improvers, corrosioninhibitors, viscosity index improvers, pour point depressants,detergents, anti-foaming agents and viscosity adjusters. Examples ofsuitable additives are included in Table D in U.S. Pat. No. 4,755,316.

[0021] The following Examples further illustrate the present invention.

EXPERIMENTAL METHOD

[0022] The apparatus used incorporated a hermetic reciprocatingcompressor, forced air cooled condenser, manual expansion valve and anevaporator enclosed in an insulated bath filled with an aqueous glycolmixture. Electrical heater elements were fitted to the bath assembly inorder to provide a heat load on the evaporator. Numerous thermocoupleswere fitted around the system to enable determination of the superheatand subcooling of the refrigerant. Pressure gauges were also fitted toallow the evaporator and condenser temperatures to be determined.

[0023] The refrigerant composition was charged to the calorimeter fromthe liquid phase cylinder access in order to avoid any shift in thecomposition. The capacity (heat extraction rate or duty) of therefrigerant compositions were determined by measuring the heat input tothe bath balanced against the heat extraction by the refrigerant. Thepower consumption of the compressor was measured enabling thecoefficient of performance (C.O.P.) to be determined. The evaporatingtemperature was 0° C., the condensing temperature 40° C. and thesuperheat 8K.

[0024] The results of formulations for R600 are shown in Table 1 withthe Performance Index in descending order. These results are showngraphically in FIG. 1 of the accompanying drawings; the numberedcontours represent the following values: Contour Key 1 = 3.4 5 = 3.0 2 =3.3 6 = 2.9 3 = 3.2 7 = 2.8 4 = 3.1 8 = 2.7

[0025] TABLE 1 Formulation / % w/w Performance % R125 % R134a % R600Duty/kW C.O.P. Index 46.5 50.0 3.5 1.89 1.83 3.46 47.0 51.5 1.5 1.861.83 3.39 50.0 46.5 3.5 1.85 1.83 3.39 47.0 51.8 1.3 1.87 1.78 3.33 40.057.5 2.5 1.80 1.82 3.28 58.9 40.1 1.0 1.91 1.70 3.25 60.0 36.5 3.5 1.881.72 3.23 59.8 38.7 1.5 1.83 1.76 3.22 46.0 52.7 1.3 1.81 1.76 3.19 50.047.5 2.5 1.82 1.75 3.19 48.0 50.8 1.2 1.79 1.76 3.15 40.0 56.5 3.5 1.771.77 3.13 39.9 58.6 1.5 1.75 1.76 3.08 60.0 37.5 2.5 1.82 1.66 3.02 39.859.3 1.0 1.69 1.68 2.84 48.9 50.1 1.0 1.57 1.61 2.53

[0026] Performance Index−Duty×C.O.P., i.e. measure of overallperformance.

[0027] Results of formulations with R600a are shown similarly in Table 2and in FIG. 2; the numbered contours represent the following values:Contour Key 1 = 3.7 6 = 3.2 2 = 3.6 7 = 3.1 3 = 3.5 8 = 3.0 4 = 3.4 9 =2.9 5 = 3.3 10 = 2.8 

[0028] TABLE 2 Formulation / % w/w Performance % R125 % R134a % R600aDuty/kW C.O.P. Index 46.0 50.0 4.0 1.91 2.04 3.90 46.5 50.0 3.5 1.781.88 3.35 47.1 51.4 1.5 1.82 1.75 3.18 49.6 49.4 1.0 1.72 1.75 3.01 38.159.9 2.0 1.70 1.74 2.96 59.4 39.6 1.0 1.75 1.62 2.82 48.6 49.4 2.0 1.711.61 2.75 39.4 59.6 1.0 1.63 1.64 2.68 60.2 37.8 2.0 1.70 1.57 2.67

1. A refrigerant composition which comprises: (a) pentafluoroethane,octafluoropropane, trifluoromethoxydifluoromethane orhexafluoro-cyclopropane, or a mixture of two or more thereof, in anamount of at least 35% based on the weight of the composition, (b)1,1,1,2- or 1,1,2,2-tetrafluoroethane,trifluoromethoxypentafluoroethane, 1,1,1,2,3,3-heptafluoropropane or amixture of two or more thereof, in an amount of at least 30% by weightbased on the weight of the composition and (c) n-butane or isobutane, inan amount from 1% to less than 2.3% by weight based on the weight of thecomposition.
 2. A composition according to claim 1 in which component(c) is present in an amount above 1.0 up to 2.0% by weight based on theweight of the composition.
 3. A composition according to claim 2 inwhich component (b) is present in an amount of about 1.5% by weightbased on the weight of the composition.
 4. A composition according toclaim 1 or 2 in which component (a) is pentafluoroethane.
 5. Acomposition according to claim 4 in which component (a) is present in anamount from 35 to 65% by weight based on the weight of the composition.6. A composition according to claim 5 in which component (a) is presentin an amount from 40 to 55% by weight based on the weight of thecomposition.
 7. A composition according to claim 6 in which component(a) is present in an amount from 45 to 52% by weight based on the weightof the composition.
 8. A composition according to any one of thepreceding claims in which component (b) is 1,1,1,2-tetrafluoroethane. 9.A composition according to claim 8 in which component (b) is present inan amount from 35 to 60% by weight based on the weight of thecomposition.
 10. A composition according to claim 9 in which component(b) is present in an amount from 45 to 60% by weight based on the weightof the composition.
 11. A composition according to claim 10 in whichcomponent (b) is present in an amount from 47.5 to 55% by weight basedon the weight of the composition.
 12. A composition according to claims4 and 8 in which both components are present in an amount from 35 to 60%by weight based on the weight of the composition.
 13. A compositionaccording to claim 12 in which both components are present in an amountfrom above 45 to 55% by weight based on the weight of the composition.14. A composition according to any one of the preceding claims in whichcomponent (c) is n-butane.
 15. A composition according to any one of thepreceding claims which comprises a further component.
 16. A compositionaccording to claim 15 in which the further component is ahydrofluorocarbon.
 17. A composition according to claim 16 in which thehydrofluorocarbon has a boiling point at atmospheric pressure of at most−40° C.
 18. A composition according to claim 16 or 17 in which the F/Hratio in the hydrofluorocarbon is at least
 1. 19. A compositionaccording to claim 18 in which the hydrofluorocarbon is difluoromethaneor trifluoromethane.
 20. A composition according to any one of claims 15to 19 in which the further component is present in an amount notexceeding 5% by weight based on the weight of (a), (b) and (c).
 21. Acomposition according to claim 20 in which the further component ispresent in an amount not exceeding 2% by weight based on the weight of(a), (b) and (c).
 22. A composition according to claim 1 substantiallyas hereinbefore defined.
 23. Use of a composition as claimed in any oneof the preceding claims as a refrigerant in a refrigeration apparatus.24. The process for producing refrigeration which comprises condensing acomposition as claimed in any one of claims 1 to 16 22 and thereafterevaporating the composition in the vicinity of a body to be cooled. 25.A refrigeration apparatus containing, as refrigerant, a composition asclaimed in any one of claims 1 to 16 22.